1. Field of the Invention
This invention relates to film deposition methods, and more particularly, to such methods for depositing a thin transparent hard film on a substrate, the properties of which may be enhanced by transformation of its surface in such manner. The invention is particularly applicable to film implantation in plastics.
2. Description of the Prior Art
With the increasing use of plastic and other non-glass lenses in eyeglasses and other items, it has become increasingly important to develop hardened surfaces on such relatively soft materials which resist scratching and abrasion. This is particularly true since the recent introduction of laws requiring the discontinuance of glass lenses in all but a few types of eyeglasses. Various methods of developing such hardened surfaces have been employed, but with less than complete success. These methods include the dipping of plastic lenses, the wiping on of a film, the use of harder plastics themselves, the provision of a laminated lens and similar approaches. Ideally, of course, such a product should have the resilience of the better plastics for protection against impact from hard objects while having surfaces that are as effective as glass or more so in resisting scratching and abrasion.
Similarly the surface properties of many materials and objects may be enhanced by the provision of an extremely thin surface coating of a suitable material which may serve to protect the surface underneath from corrosion, wear and the like or provide a surface hardness not attainable by the substrate alone. Thus for example, razor blades which are said to suffer more from corrosion than wear, may be made to last many times longer than at present with suitable protection of the fine cutting edge from corrosion. If at the same time the cutting edge may be hardened, then the effects of wear will be reduced as well, both factors acting together to provide a much longer lasting blade.
In addition, surface alloys may be developed on metal substrates and surface layers of various dopings of impurities and the like on semiconductor substrates may be possible through the use of appropriate deposition and implantation techniques. The accomplishment of such developments would greatly economize on the use of rare and expensive materials where only surface effects are needed.
Efforts have been made to develop such products by particle bombardment. Examples of such may be found in U.S. Pat. Nos. 3,117,022 of G. A. Bronson et al., 3,494,852 of M. Doctoroff, 3,371,649 of H. E. T. Gowen, 3,409,529 of K. L. Chapra et al., 3,472,751 of W. J. King, 3,562,141 of J. R. Morley, and others. However, whether through ineffective focusing or direction of the beam, emission and control of the ionized particles or for whatever reason unknown, such approaches have not resulted in truly acceptable and satisfactory products which realized the potential of the theories underlying such bombardment techniques.